Beam Irradiation apparatus, beam irradiation method, and method for manufacturing thin film transistor

ABSTRACT

A galvanometer mirror rotates in one direction when the galvanometer mirror is used. A spot can be scanned on an irradiated surface at a more constant speed by rotating the galvanometer mirror and by using the inertia. Moreover, it is preferable to make the galvanometer mirror heavy because the inertia becomes higher so that the spot is scanned at a more constant speed. In addition, in a polygon mirror of this invention, mirrors are arranged so as not to contact each other because a change time of the scanning position between the mirrors is provided. By moving the irradiated object with timing together when the laser light is not irradiated, the laser process can be performed efficiently.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a beam irradiation apparatus and a beamirradiation method. Moreover, the present invention relates to a methodfor manufacturing a thin film transistor using the apparatus and themethod.

2. Description of Related Art

In recent years, a research has been conducted concerning a thin filmtransistor having a channel-forming region in a poly-crystallinesemiconductor film (hereinafter this thin film transistor is referred toas a poly-crystalline TFT) as a semiconductor element in a displaydevice, an integrated circuit, or the like. With the development of thedisplay device and the integrated circuit, further enhancement of thecharacteristic of the poly-crystalline TFT has been demanded.

Consequently, as one means to obtain the poly-crystalline TFT, a laserirradiation apparatus including a continuous wave laser and means forscanning a laser beam (also referred to as laser light) is used tocrystallize the semiconductor film. (For example, refer to a patentdocument 1)

Moreover, a galvanometer mirror (refer to a patent document 2) or apolygon mirror (refer to a patent document 3) is often used as the meansfor scanning the laser light. This is because the galvanometer mirrorand the polygon mirror can increase the scanning speed easily. This canreduce the burden on the apparatus.

FIG. 7 shows a structure of a conventional galvanometer mirror. Laserlight 72 emitted from a laser light oscillator 71 is reflected by agalvanometer mirror 73 and a spot (irradiated region) 75 is formed on anirradiated object 74. The laser irradiation process is performed in sucha way that the spot 75 is scanned on the irradiated object by vibratingthe galvanometer mirror 73 at amplitude of vibration 76. The laser lightis irradiated to the irradiated object in accordance with the amplitudeof vibration of the galvanometer mirror shown in FIG. 7.

In addition, in the case of the polygon mirror, the laser light isirradiated to the irradiated object by rotating a plurality of mirrorsprovided so as to contact.

Patent Document 1

Japanese Patent Laid-Open No. 2003-86505

Patent Document 2

Japanese Patent Laid-Open No. 2003-86507

Patent Document 3

Japanese Patent Laid-Open No. 2003-45890

SUMMARY OF THE INVENTION

In particular, when the mass production using a large substrate isconsidered, it is emphasized to obtain the crystalline semiconductorfilm that is uniform over a wide range efficiently. Consequently, thescanning means such as the galvanometer mirror or the polygon mirror isoften employed which can easily increase the scanning speed because ofthe lightness in weight. In addition, the burden on the laserirradiation apparatus can be reduced by these scanning means.

However, the use of the above scanning means might cause a problem thatthe scanning speed and the irradiated state are not uniform in the endportions of the irradiated surface where the scanning starts and thescanning ends. In addition, the vibration of the galvanometer mirrormight make the scanning width meander.

For example, when the laser irradiation is performed to thesemiconductor film by reflecting the laser light on the galvanometermirror doing the pendulum movement (vibration), the speed decreasestoward the point where the direction of the pendulum movement changes(the point is also referred to as a peak of the pendulum movement or apoint where the galvanometer mirror stops) and at last the speed becomeszero for a moment. After that, the speed increases gradually whilechanging the moving direction. Although the galvanometer mirror canincrease or decrease the scanning speed in a short time, the presentinventor recognized that such inhomogeneous laser irradiation, which isthe irradiation unevenness, leads to a problem as higher-quality andmore uniform crystallization of the semiconductor film is required.Since the energy was irradiated excessively to the irradiated object dueto such irradiation unevenness, there was concern such that theirradiation unevenness might cause the peeling of the amorphoussemiconductor film. When the film is peeled, it was concerned that eventhe normal film is rough by the spattered semiconductor film. Thus, thepresent inventor recognized that inhomogeneous scanning speed of thelaser light is a problem in the field of semiconductor wherehigh-quality and uniform crystallization of the semiconductor film isrequired.

In addition, in the case of using a polygon mirror doing a rotationalmovement in which a plurality of mirrors is connected continuously, theirradiation position differed slightly depending on the incidence angleof the laser light reflected by each mirror. In particular, thedifference of the incidence angle at the boundary between the mirrorscaused the difference in the positions where the scanning starts and thescanning ends and further caused the inhomogeneous laser irradiationprocess. In addition, since the irradiation position also differs in adirection perpendicular to the scanning direction, this also caused theinhomogeneous laser irradiation process. The present inventor recognizedthat the inhomogeneous laser light irradiation becomes a problem whenhigher-quality and more uniform crystallinity of semiconductor film isobtained.

Consequently, it is an object of the present invention to provide a beamirradiation apparatus and a beam irradiation method that homogenize thescanning speed of the scanning means such as the galvanometer mirror orthat control the scanning position accurately. In addition, it is anobject of the present invention to provide uniform laser annealing(including crystallization and activation) to a thin film transistor(hereinafter referred to as a TFT) or the like using the above beamirradiation apparatus and the above beam irradiation method.

In the present invention made in view of the above problems, whenscanning (deflecting) means having singular specular body (also referredto as a mirror) is used, the scanning means rotate in one direction. Itis noted that the specular body has a plane surface or a curved surface.Hereinafter, the galvanometer mirror is taken as an example of such aspecular body.

The galvanometer mirror of the present invention rotates stably becauseit rotates in one direction, and the vibration of the mirror due to thechange in acceleration is eliminated. When the galvanometer mirror is inthe position where the laser light is not irradiated, the irradiatedobject may move in a Y-axis direction, which is perpendicular to anX-axis direction assuming that the X-axis direction is the movingdirection of the spot by the galvanometer mirror. Then, the laser lightcan be scanned in XY-axes directions, and therefore the laserirradiation process can be performed to the large substrate. On thisoccasion, since the galvanometer mirror rotates in one direction, thelaser light is scanned in only one direction on the X-axis of theirradiated object.

Specifically, a mirror surface rotates on the shaft arranged in agalvanometer mirror 13 as its center as shown in FIG. 1. The shaft has asupporting bar in one end or in both ends and has an apparatus forcontrolling the rotation. It is preferable that the supporting bar isprovided in the both ends because the rotation axis is more stable.Laser light 12 emitted from an oscillator 11 is reflected on agalvanometer mirror 13, and a spot 15 is formed on an irradiated object14. The spot moves by rotating such a galvanometer mirror 13, and thusthe laser irradiation process is performed to the irradiated object.

As thus described, the spot can be scanned at more constant speed on theirradiated surface by rotating the galvanometer mirror and by usinginertia. In addition, since the heavier galvanometer mirror produces thehigher inertia, it is preferable that the galvanometer mirror is heavyso that the spot is scanned at much more constant speed. Furthermore,since the galvanometer mirror can have a simple and compact structure,the galvanometer mirror is preferable when it is installed in the laserirradiation apparatus.

As another scanning means, scanning means having a plurality of specularbodies (this scanning means is referred to as a polygon mirror forsimplicity) is given. A polygon mirror of the present invention has aplurality of mirrors 27 as shown in FIG. 2. In order to provide time forscanning in the Y-axis direction in accordance with mirror interval, theplurality of mirrors is arranged so that they do not contact each other,which means the side surface of the mirror does not contact each other.The laser light 22 is incident into the polygon mirror 23 that rotateson the shaft as its center, and the spot 25 is scanned on the irradiatedobject 24. As a result, there are alternately times when the irradiatedobject 24 is irradiated by the spot 25 and times when it is notirradiated by the spot 25. In other words, when the laser light isincident into the boundary between the mirrors, the laser light is notirradiated to the irradiated object. The laser irradiation process canbe performed efficiently by moving the irradiated object when the laserlight is not irradiated thereto. In other words, when the spot isscanned in the X-axis direction by the polygon mirror and when the spotdisappears (when the laser light is not irradiated), the irradiatedobject is moved in the Y-axis direction. On this occasion, since thedirection in which the laser light is reflected is different little bylittle depending on each mirror in the polygon mirror, the irradiatedposition and the like are compensated by changing the travel amount ofthe irradiated object in the Y-axis direction. Accordingly, since it isno longer necessary to set a compensating lens between the polygonmirror and the irradiated object, the laser irradiation apparatus can besimplified and be preferable.

According to such scanning means of the present invention, uniform laserirradiation can be performed to the irradiated object. When thesemiconductor film is employed as the irradiated object, it is possibleto form the poly-crystalline TFT having uniform crystallinity anduniform electrical characteristic.

It is noted that the present invention can use a continuously outputenergy beam (hereinafter referred to as a CW beam). As the CW beam, asolid-state laser may be used. For example, a beam emitted from a YVO₄laser, a YAG laser, a YLF laser, a YAlO₃ laser, an Ar laser, or the likecan be applied. In addition, a harmonic of these lasers may be alsoemployed. When the laser is employed as the light source, the CW beam isreferred to as a CW laser.

It is noted that although the laser beam may have any shape, it ispreferable that the laser beam is shaped to be linear by transmittingthrough an optical system. The term “linear” herein used does not mean aline in a strict sense but means a rectangle having a large aspect ratio(or an oblong shape). For example, the linear indicates the rectanglehaving an aspect ratio of 10 or more (preferably in the range of 100 to10000). Specifically, the spot diameter of the linear laser beam has alength ranging from 150 to 1000 μm in the major axis and a lengthranging from 5 to 20 μm in the minor axis. With the laser beam shapedinto linear, the process can be performed at high throughput.

As above, the present invention can remove inhomogeneity of theirradiation of the laser beam caused by the operation of the scanningmeans and can provide a poly-crystalline TFT having uniformcrystallinity and uniform electrical characteristic. Even though theirradiated object has a large size, the poly-crystalline TFT havinguniform characteristic over a wide range can be formed, and therefore itis possible to improve the mass productivity of the display device andthe integrated circuit.

ADVANTAGEOUS EFFECT OF THE INVENTION

Uniform laser irradiation can be performed to the irradiated objectaccording to the present invention. When the semiconductor film is usedas the irradiated object, the poly-crystalline TFT having uniformcrystallinity and uniform electric characteristic can be formed.Moreover, since the beam spot can be scanned at a constant speed on theirradiated object and since the scanning position of the spot can becontrolled accurately, uniform laser annealing can be performed to thesemiconductor film. Furthermore, when the large substrate is used, thepresent invention is preferable because the laser annealing can beperformed very efficiently.

In addition, when the polygon mirror of the present invention is used,much more uniform laser irradiation can be performed by setting thetravel amount of the XY stage mirror by mirror.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing for showing the laser irradiation apparatus of thepresent invention.

FIG. 2 is a drawing for showing the laser irradiation apparatus of thepresent invention.

FIG. 3 is a drawing for showing the laser irradiation method of thepresent invention.

FIGS. 4A-4B are drawings showing the laser irradiation method of thepresent invention.

FIGS. 5A-5B are drawings showing the light-emitting device formed usingthe laser irradiation method of the present invention.

FIGS. 6A-6E are drawings showing the electronic instruments formed usingthe laser irradiation method of the present invention.

FIG. 7 is a drawing for showing the conventional laser irradiationmethod.

FIGS. 8A-8B are drawings showing the laser irradiation apparatus of thepresent invention.

EMBODIMENT MODES OF THE INVENTION

Embodiment modes of the present invention are hereinafter explainedbased on drawings. However, since the present invention can be embodiedin many different modes, it is easily understood by those skilled in theart that the modes and the details can be changed and modified invarious ways unless such changes and modifications depart from the scopeand the content of the present invention hereinafter defined. Thus, thepresent invention is not limited to the description of the embodimentmodes. In addition, the same reference numeral is given to the same partor the part having the similar function throughout the all drawings forexplaining the embodiment modes, and the explanation to such a partshall not be repeated.

Embodiment Mode 1

The present embodiment mode explains the case where a rotatinggalvanometer mirror is used as the scanning means and a semiconductorfilm is used as the irradiated object and where a poly-crystalline TFTis formed by crystallizing the semiconductor film.

FIG. 3 shows a laser irradiation apparatus including an oscillator 101for emitting a CW laser (also referred to as a continuous wave laser),an optical system 102 for shaping a laser beam emitted from theoscillator into linear, a galvanometer mirror for scanning the linearlaser beam on a semiconductor film, a shaft 108 for rotating thegalvanometer mirror, a control apparatus 110 for controlling the shaftand the rotation of the galvanometer mirror, and an fθ lens 104 formaking the shape of the laser beam on the irradiated surface constant.The laser beam emitted from the oscillator is incident into the opticalsystem so that its shape becomes linear laser beam (hereinafter thisbeam is referred to as a linear beam). Then the linear beam is incidentinto the rotating galvanometer mirror and is reflected thereby. Afterthat, the linear beam is irradiated to the irradiated object through thefθ lens. The irradiation of the laser beam is controlled by thestructure having the above function.

For example, the optical system 102 arranges a planoconcave lens havinga focal length of 50 mm, a planoconvex lens having a focal length of 200mm, a planoconvex cylindrical lens having a focal length of 250 mmbehind the planoconvex lens, and a planoconcave cylindrical lens havinga focal length of 100 mm behind the planoconvex cylindrical lens. It isnoted that the direction of curvature of the planoconcave cylindricallens is the same as that of the planoconvex cylindrical lens. The laserbeam is shaped into the linear beam by transmitting through the opticalsystem and by being condensed repeatedly. In addition, a lens except forthe above lenses may be arranged so that a spot of the laser beam on theirradiated surface (also referred to as a beam spot) has a desired shape(for example linear).

The control apparatus 110 for controlling so that the galvanometermirror 103 rotates in one direction is provided. A motor or the like canbe used as the means for rotating the galvanometer mirror. Then, inorder to make the rotation speed more constant using the inertia, theweight of the galvanometer mirror may be made heavy.

The laser beam scanned by the galvanometer mirror transmits through thefθ lens 104 so that the laser beam has constant shape on thesemiconductor film. Then, the laser beam is incident into thesemiconductor film and is scanned along a moving route 107. It is notedthat when the galvanometer mirror rotates in one direction, the movingroute 107 is only one direction. When the rotating direction changes,the direction of the moving route 107 becomes the opposite of the onedirection.

In such laser irradiation, when the laser beam is not irradiated to thesemiconductor film, which means when the beam spot 105 is not on thesemiconductor film 106, the stage 109 moves in the Y-axis direction(indicated by an arrow 112) to change the scanning position of the spot105. By repeating such an operation, it is possible to perform the laserirradiation, which is the laser annealing, uniformly in Y-axisdirection. Subsequently, in the case where the next line in thesemiconductor film is irradiated, the irradiated object moves in theX-axis direction (indicated by an arrow 111), and then the same processis performed. In addition, on this occasion, it is necessary that thebeam spot is scanned in such a way that the rotation of the galvanometermirror and the moving of the stage in the Y-axis direction aresynchronized.

Since the semiconductor film is not irradiated when a scanning speed ofthe laser beam is not uniform according to the above irradiation method,it is possible to obtain the poly-crystalline TFT having more uniformcrystallinity and more uniform electrical characteristic.

After that, the process that is necessary for forming the TFT isperformed as appropriate, and thus an active matrix substrate in which aplurality of poly-crystalline TFTs is formed can be provided. When thepoly-crystalline TFT is formed using a large substrate, multiple panelscan be obtained and therefore the manufacturing cost can be reduced. Itis noted that the laser irradiation method of the present invention canbe applied to the laser annealing including crystallization andactivation process of a semiconductor film.

Embodiment Mode 2

The present embodiment mode explains a case where the mass productivityof the thin film transistor is enhanced by performing a laser process toa semiconductor film formed over a substrate using a plurality of laseroscillators. It is noted that a polygon mirror is used as the scanningmeans in the explanation.

FIG. 4 shows an example where three CW laser oscillators 201, threetelecentric fθ lenses 204, and three polygon mirrors 203 are used toperform the laser annealing to a semiconductor film 205 formed over alarge substrate having a size of 1500 mm×1800 mm. It is noted that FIG.4(A) is a top view, and (B) is a side view.

An oxide film (a silicon oxide film such as SiON or SiO₂) is formed on asubstrate as a base film and then a semiconductor film is formed thereonsequentially. The semiconductor film may be formed of a silicon-basedmaterial by a CVD method, a sputtering method, or the like. In thisembodiment mode, an amorphous silicon film is formed by the CVD methodusing silane gas. In some film-forming methods, the semiconductor filmmay contain too much density of hydrogen to resist the laser annealing.Therefore, in order to increase the resistivity probability of thesemiconductor film against the laser annealing, the density of hydrogenin the semiconductor film is preferably made on the order of 10²⁰/cm³ orless. Therefore, when the film contains hydrogen more than the abovevalue at the time of completion of the film-forming, it is preferable todehydrogenate by the thermal annealing at temperatures ranging fromapproximately 400 to 500° C. for about one hour. The laser annealing isperformed to the semiconductor film formed thus. It is noted that thesemiconductor film may be patterned into the fixed shape before thelaser annealing.

For example, the second harmonic (wavelength 532 nm) of an LD-pumped CWNd:YVO₄ laser is used as the laser oscillator 201. The laser oscillator201 has an output power of 10 W and is TEM00 mode. The laser beam spothas a diameter φ of 2.3 mm and has a divergence angle of 0.35 mrad.

Since this wavelength is transparent to the amorphous silicon film andthe substrate, it may be necessary to devise a method for suppressingthe inhomogeneous laser annealing due to the interference. In that case,the laser beam is preferably made incident into the semiconductor film205 at an angle except 0°, for example. On this occasion, theappropriate incidence angle depends on the shape or the size of the beamspot. The direction to which the laser spot 208 is extended(corresponding to the major axis) is the Y-axis direction in FIG. 4.Although it may be extended to another direction according to thepurpose, it is preferable to extend it in the Y-axis direction in orderto maximize the throughput in this embodiment mode. For example, whenthe laser beam spot shaped into a linear ellipse having a size of 400 μmin its major axis and 20 μm in its minor axis on the semiconductor film205 is set so that the major axis thereof is included in the incidenceplane, the appropriate incidence angle θ is approximately 20°.

For example, the optical system 202 includes a planoconcave lens havinga focal length of 50 mm, a planoconvex lens having a focal length of 200mm positioned 145 mm apart, a planoconvex cylindrical lens having afocal length of 250 mm positioned 140 mm behind the planoconvex lens,and a planoconcave cylindrical lens having a focal length of 100 mmpositioned 145 mm behind the planoconvex cylindrical lens. It is notedthat the direction of curvature of the planoconvex cylindrical lens isthe same as that of the planoconcave cylindrical lens. Moreover, apolygon mirror 203 is arranged approximately 250 mm behind theplanoconcave cylindrical lens and a telecentric fθ lens 204 is arrangedin accordance with the specifications of these lenses. The telecentricfθ lens 204 has a focal length of approximately 300 mm and has adiameter φ of 120 mm.

In the laser irradiation apparatus having the optical system as above,the beam spot 208 extended to be linear on the semiconductor film 205 isscanned on the semiconductor film 205 at a speed of 500 mm/s by thepolygon mirror 203. Since the polygon mirror of the present inventiondoesn't contact each other at the boundary, there is time for changingthe scanning position on the semiconductor film.

When the irradiated region of the laser beam scanned by one mirror inthe polygon mirror has a width of 100 mm, the beam spot 208 is scannedin such a way that after the beam spot 208 is scanned 100 mm by thepolygon mirror in the X-axis direction, an XY stage 206 is moved 200 μm(the width of the crystallized region in a direction perpendicular tothe scanning direction of the beam spot determined by the size of thebeam spot) in the Y-axis direction, and then the beam spot is scanned onthe semiconductor film 205 by the polygon mirror 203.

In particular, when the polygon mirror is used, it is preferable toadjust the travel amount of the stage mirror by mirror. This is becausethe polygon mirror has a plurality of mirrors so that the angle to whichthe beam is reflected may be different in each mirror. This method isexplained in detail in an embodiment mode 3. In the laser irradiation asabove, the region in the semiconductor film not irradiated by the laserbeam depends on the laser beam or the scanning means such as the polygonmirror, and the travel amount of the stage may be set appropriately inevery embodiment.

The laser annealing is performed to a region A in the figure byrepeating the above. The number of regions A conforms to the number oflaser oscillators and the interval between the regions A is set to 100mm appropriately, for example. After the laser annealing to the regionA, the semiconductor film 205 is moved by an XY stage 206 to theposition where a region B can be annealed. Then, the laser annealing isperformed to the region B at a constant width of 100 mm in the same way.A series of these operations can perform the laser annealing to thewhole surface of the semiconductor film 205. Of course, it is notnecessary to perform the laser, annealing all over the semiconductorfilm 205. It is preferable to perform the laser annealing only to thenecessary part thereof because the processing time can be shortened. Insuch a case, it is necessary to provide a positioning mechanism and thelike precisely and a practitioner may calculate the necessary precisionto determine its structure appropriately.

In the present embodiment mode, a telecentric fθ lens is used so thatthe laser beam is incident into the semiconductor film at a constantincidence angle. This provides the uniformity of the laser annealing.When the uniformity is not required, an fθ lens may be usedalternatively. In this embodiment mode, a plurality of telecentric fθlenses 204 is arranged at intervals. Therefore, the semiconductor filmcan be irradiated with a plurality of laser beams simultaneously withoutthe adjacent telecentric fθ lenses interfering with each other.

The semiconductor film is thus crystallized. Subsequently, after thesemiconductor film is patterned into the fixed shape as needed, a gateinsulating film, a gate electrode, and an impurity region are formed,and then activation is performed. The laser irradiation apparatus andthe laser irradiation method of the present invention can be alsoapplied to activate the semiconductor film. Then an interlayerinsulating film, a source wiring, a drain wiring, a pixel electrode, andthe like are formed, and thus an active matrix substrate having aplurality of thin film transistors is formed. In addition, the activematrix substrate can be used to form a liquid crystal display device, alight-emitting device, another display device having a display portion,or a semiconductor integrated circuit.

As above, the present invention can provide high throughput comparedwith the case in which only one laser oscillator is employed. Therefore,the present invention is suitable to the laser annealing of thesemiconductor film formed over a large substrate. As a result, the massproductivity of the thin film transistor can be enhanced.

Although the present embodiment uses a plurality of laser oscillators, alaser beam emitted from one laser oscillator may be divided by a mirroror the like to form a plurality of spots.

Moreover, although the present embodiment mode uses the polygon mirroras the scanning means, the galvanometer mirror having the rotatingfunction can be used.

Embodiment Mode 3

The present embodiment mode explains the timing for moving the XY stageand the polygon mirror with reference to FIG. 8. It is noted that thepolygon mirror has N number of specular bodies (1≦n≦N:n is an integernumber).

In the scanning means such as the polygon mirror having a plurality ofmirrors, the reflection angle may be different mirror by mirror.Although the XY stage moves at a constant interval under thiscircumstance, the interval between the scanning positions is no longerconstant and therefore uniform laser irradiation cannot be performed.Consequently, as shown in the present embodiment mode, the distancebetween the mirrors in the polygon mirror, which means the travel amountof the XY stage when the laser beam is not irradiated, is set mirror bymirror. Uniform laser irradiation is performed by reflecting the laserlight sequentially on the mirror.

In other words, as shown in FIG. 8(A), in the optical system where apolygon mirror 83 scans laser light 82 emitted from an oscillator 81, aspot (n) formed by a mirror (n), a spot (n+1), a spot (n+2) . . . arescanned sequentially in one direction of the X-axis direction byrotating the polygon mirror 83 on a shaft 85 as a center, and thus thelaser irradiation process is performed to the surface of the irradiatedobject 84. As shown in FIG. 8(B), when the travel amount of the XY stagemoving from the mirror (n) to the next mirror is expressed with Y(N), itis preferable that Y(1), Y(2), . . . Y(M) are set respectively. It isnoted that N is the number of mirrors.

In order to set the travel amount Y(n), Y(n+1) . . . of the XY stage,each of the plurality of mirrors is numbered and the mirror is scannedonce, for example. After a reflection angle of each mirror isunderstood, the travel amount of the stage is determined based on this.Each travel amount may be input into the control apparatus of the XYstage.

Thus, when the travel amount of the XY stage in X-axis direction and thetiming for moving the XY stage in X-axis direction are set in accordancewith the reflection angle of each mirror in the polygon mirror and withthe travel amount of the irradiated object between the mirrors, moreuniform laser irradiation process can be performed.

It is noted that this embodiment mode can be also applied to the polygonmirror in which the mirrors are provided so as to contact. In otherwords, uniform laser irradiation can be performed by adjusting thetravel amount of the XY stage when the XY stage moves at the boundarybetween the mirrors provided so as to contact each other. In addition,when the time for moving the stage in Y-axis direction is necessary, themeans for blocking the laser beam in one end, in the other end, or inboth ends of the scanning of the laser beam may be provided.

Embodiment Mode 4

The present embodiment mode explains a light-emitting devicemanufactured using the active matrix substrate with reference to FIG. 5.

FIG. 5(A) is a cross-sectional view of a light-emitting device,specifically an EL module. FIG. 5(B) is an enlarged view of thelaminated-layer structure of the light-emitting element (having anorganic compound layer (also referred to as an EL layer), a firstconductive film, and a second conductive film) of the EL module.

FIG. 5(A) shows a first substrate 400, a base insulating film 401, a TFT422 formed by the laser annealing with the use of the laser irradiationapparatus of the present invention, a first conductive film (electrode)403, an insulator (also referred to as a partition wall, a barrier, anembankment, or a bank) 404, an organic compound layer 405, a secondconductive film (electrode) 406, a protective film 407, an airspace 408,and a second substrate 409.

A glass substrate, a quartz substrate, a silicon substrate, a plasticsubstrate, a metal substrate, a stainless substrate, a flexiblesubstrate, or the like can be used as the first substrate and the secondsubstrate. The flexible substrate is a film-like substrate formed ofPET, PES, PEN, acryl, or the like, and when the flexible substrate isused to manufacture a light emitting device, weight saving isanticipated. It is desirable to form a barrier layer such as an aluminumfilm (AlON, AlN, AlO, or the like), a carbon film (DLC or the like), orSiN on a surface of the flexible substrate or on both the surface andthe rear surface thereof in a single layer or in multi-layers becausethe durability and the resistivity against gas can be improved.

In addition, either the first conductive film or the second conductivefilm is formed of a light-transmitting conductive film, for example ITO,according to whether the light from the organic compound is emittedupward or downward. When the light is emitted to both upward anddownward, both the first conductive film and the second conductive filmare formed of the light-transmitting conductive film.

The TFT 422 (p-channel TFT in this embodiment mode) provided over thefirst substrate 400 is an element for controlling the current flowingthrough the organic compound layer 405. The TFT 422 has an impurityregion 411 functioning as a drain region (or a source region dependingon the polarity), a channel-forming region 412, and a gate electrode 417provided over the channel-forming region. Furthermore, the TFT 422 has adrain electrode (or a source electrode) 416, which is connected to adrain region (or a source region) for connecting the impurity region 411and the first conductive film 403 electrically. Moreover, a wiring 418such as a power supplying line or a source wiring can be formedsimultaneously in the same process for forming the drain electrode 416.

A base insulating film 401 (herein the base insulating film is formed ofan insulating nitride film as a lower layer and an insulating oxide filmas an upper layer) is formed over the first substrate 400 and a gateinsulating film is provided between the gate electrode 417 and thesemiconductor film. In addition, an interlayer insulating film 402 isformed of an organic material or an inorganic material. Although it isnot illustrated in the figure, one TFT or a plurality of TFTs (n-channelTFT or p-channel TFT) is further provided in one pixel. In addition,although this embodiment mode showed the TFT having one channel-formingregion 412, there is no particular limitation, and the TFT may have aplurality of channels, which is called a multi-channel TFT.

In addition, although this embodiment mode explained a top-gate type TFTas the example, the present invention can be applied regardless of theTFT structure. For example, the present invention can be applied to abottom-gate type (inversely staggered) TFT and a staggered TFT.

In addition, the first conductive film 403 becomes an anode (or acathode) of the light-emitting element. When the first conductive filmis formed of a transparent conductive film, ITO (alloy of indium oxideand tin oxide), alloy of indium oxide and zinc oxide (In₂O₃—ZnO), zincoxide (ZnO), or the like can be used.

In addition, there is an insulator 404 (also referred to as a bank, apartition wall, a barrier, an embankment, or the like) covering the endportion of the first conductive film 403 (and the wiring 418). Theinsulator 404 can be made of an inorganic material (silicon oxide,silicon nitride, silicon oxynitride, or the like), a photosensitive ornon-photosensitive organic material (polyimide, acryl, polyamide,polyimidamide, resist, or benzocyclobutene), or the layers formed bylaminating these materials. This embodiment mode uses a photosensitiveorganic resin covered by the silicon nitride film. For example, when thepositive photosensitive acrylic is used as the material of the organicresin, it is preferable that only the upper end portion of the insulatorhas the radius of curvature. In addition, the insulator may be either anegative type, which becomes insoluble in the etchant by the light, or apositive type, which becomes soluble in the etchant by the light.

In addition, the organic compound layer 405 is formed by a vapordeposition method, an ink jet method, or a coating method. In thisembodiment mode, the organic compound layer is formed in a vapordeposition apparatus to obtain uniform film thickness. For example, whenthe vapor deposition method is used, the film is deposited in thefilm-forming chamber that is vacuum pumped so that the degree of vacuumis 5×10⁻³ Torr (0.665 Pa) or less, preferably in the range of 10⁻⁴ to10⁻⁶ Pa. At the deposition, the organic compound is vaporized by heatingit in advance, and it is spattered toward the substrate by opening theshutter. Vaporized organic compound is spattered upward and depositedthrough an opening provided in a metal mask. In order to enhance thereliability, it is preferable to degas by means of vacuum heating (attemperatures ranging from 100 to 250° C.) just before forming theorganic compound layer 405.

As shown in FIG. 5(B), the organic compound layer 405 is a laminatedlayer of HIL (a hole injecting layer), HTL (a hole transporting layer),EML (an emitting layer), ETL (an electron transporting layer), and EIL(an electron injecting layer) that are laminated in order from the anodeside. Typically, CuPc is used as the HIL, α-NPD is used as the HTL, BCPis used as the ETL, and BCP:Li is used as the EIL. It is noted that theorganic compound may have an inorganic material or may have a mixedmaterial of the organic material and the inorganic material.

In addition, in the case of a full color display, the materials eachshowing the light emission of red (R), green (G), and blue (B)respectively as the organic compound layer (EL layer) 405 can be formedselectively by the vapor deposition method using respective depositionmasks or by an ink-jetting method appropriately. Specifically, CuPc orPEDOT is used as the HIL, α-NPD is used as the HTL, BCP or Alq₃ is usedas the ETL, and BCP:Li or CaF₂ is used as the EIL. In addition, forexample, Alq₃ with dopant corresponding to each emitting color of R, Gand B (DCM or the like in the case of R, DMQD or the like in the case ofG) doped may be used as EML. It is noted that the organic compound layeras mentioned above is not limited to the laminated-layer structure, andit may be a single-layer structure.

More specific laminated-layer structure of the organic compound layer isexplained as follows. In the case of forming the organic compound layer405 to show red light emission, for example after forming CuPc in 30 nmthick and α-NPD in 60 nm thick, the same mask is used to form Alq₃ withDCM₂ and rubrene added in 40 nm thick as a red light-emitting layer.After that, BCP is formed as the electron transporting layer in 40 nmthick, and then BCP with Li added is formed in 1 nm thick as theelectron injecting layer. In addition, in the case of forming theorganic compound layer showing green light emission, for example afterforming CuPc in 30 nm thick and α-NPD in 60 nm thick, the samedeposition mask is used to form Alq₃ with coumarin 545T added in 40 nmthick as a green light-emitting layer. After that, BCP is formed in 40nm thick as the electron transporting layer, and then BCP with Li addedis formed in 1 nm thick as the electron injecting layer. In addition, inthe case of forming a layer including the organic compound layer showingblue light emission, for example after forming CuPc in 30 nm thick andα-NPD in 60 nm thick, the same mask is used to formbis[2-(2-hydroxyphenyl)benzoxazolate]zinc: Zn(PBO)₂ in 10 nm thick as anemitting layer. After that, BCP is formed in 40 nm thick as the electrontransporting layer, and then BCP with Li added is formed in 1 nm thickas the electron injecting layer. Among the organic compound layers ofthese colors, CuPc and α-NPD common to all the colors can be formed allover the pixel portion. In addition, the mask can be shared among thesecolors. For example, after forming the red organic compound layer, themask is moved to form the green organic compound layer. Then the mask ismoved again to form the blue organic compound layer. It is noted thatthe order of the organic compound layer of each color to be formed maybe set appropriately.

In addition, in the case of white light emission, the full color displaymay be achieved by providing a color filter or a color conversion layerseparately. The color filter or the color conversion layer with respectto the white light emitting upward may be pasted to the first substrateafter providing it to the second substrate. In addition, the colorfilter or the color conversion layer with respect to the white lightemitting downward can be formed through the insulating film afterforming the drain electrode (or the source electrode) 416. After that,because the insulating film and the second conductive film may be formedin order over the color filter or the color conversion layer, and thedrain electrode (or the source electrode) 416 may be connected to thesecond conductive film through a contact formed in the insulating film.

It is possible to provide a light-emitting device having the highlyhomogeneous crystalline semiconductor film according to the galvanometermirror or the polygon mirror of the present invention. As a result, itis possible to provide the light-emitting device in which theinhomogeneous laser beam irradiation (which leads to the displayunevenness) is reduced in the display portion.

It is noted that the active matrix substrate of the present inventioncan be applied not only to the light-emitting device but also to theliquid crystal display device and another display device, and further tothe semiconductor integrated circuit and CPU.

Embodiment Mode 5

The active matrix substrate manufactured by the present invention can beapplied to various kinds of electronic instruments. As the electronicinstrument, there are a portable information terminal (a mobile phone, amobile computer, a mobile game machine, an electronic book, or thelike), a video camera, a digital camera, a goggle type display, adisplay device, a navigation system, and the like. FIG. 6 shows specificexamples of these electronic instruments.

FIG. 6(A) is a display including a chassis 4001, an audio output portion4002, a display portion 4003, and the like. The active matrix substrateformed by the present invention can complete the display portion 4003having a liquid crystal material or a light-emitting element. Thedisplay device includes all the information display devices for apersonal computer, for TV broadcast reception, for advertisementdisplay, and the like.

FIG. 6(B) is a mobile computer including a main body 4101, a stylus4102, a display portion 4103, an operation button 4104, an externalinterface 4105, and the like. The active matrix substrate formed by thepresent invention can complete the display portion 4103 having a liquidcrystal material or a light-emitting element.

FIG. 6(C) is a game machine including a main body 4201, a displayportion 4202, an operation button 4203, and the like. The active matrixsubstrate formed by the present invention can complete the displayportion 4202 having a liquid crystal material or a light-emittingelement. FIG. 6(D) is a mobile phone including a main body 4301, anaudio output portion 4302, an audio input portion 4303, a displayportion 4304, an operation switch 4305, an antenna 4306, and the like.The active matrix substrate formed by the present invention can completethe display portion 4304 having a liquid crystal material or alight-emitting element.

FIG. 6(E) is an electronic book reader including a display portion 4401and the like. The active matrix substrate formed by the presentinvention can complete the display portion 4401 having a liquid crystalmaterial or a light-emitting element.

As above, the present invention can be applied in a wide range, and canbe applied to the electronic instruments in every field. In particular,it is possible to make the electronic instrument lightweight and thinwhen the flexible substrate is used as the insulating substrate of theactive matrix substrate

Embodiment Mode 6

The present invention is applied not only to the CW beam but also to theoutput energy beam in a pulse oscillation (a pulsed beam, particularlyreferred to as a pulsed laser when using the laser as the light source).

The pulsed laser in the present invention is controlled so that acrystal grain grown continuously toward the scanning direction can beobtained by oscillating the laser light at such the oscillationfrequency that the next laser light is irradiated within the period fromthe time the semiconductor film is melted with the laser light until thesemiconductor film is solidified. In other words, the present inventioncan employ a pulsed beam in which the lower limit of an oscillationfrequency is determined so that the period of a pulse oscillation(oscillation frequency) becomes shorter than the period from the timethe semiconductor film is melted until the semiconductor film iscompletely solidified.

For example, the pulsed laser using the laser as the light source has anoscillation frequency of 10 MHz or more, frequency band is considerablyhigher than that of the pulsed laser to be used usually having anoscillation frequency in the range of several tens to several hundredsHz.

It is said that it takes several tens ns to several hundreds ns tosolidify the semiconductor film completely after the semiconductor filmis irradiated with the laser light. With the pulsed laser light havingsuch a high oscillation frequency applied thereto, it is possible toirradiate the next pulsed laser light within the period from thesemiconductor film is melted by the laser light until the semiconductorfilm is solidified. Therefore, unlike the case using the conventionalpulsed laser, the interface between the solid phase and the liquid phasecan be moved continuously in the semiconductor film, thereby forming thesemiconductor film having a crystal grain grown continuously toward thescanning direction. Specifically, it is possible to form an aggregationof crystal grains, each of which has a width ranging from approximately10 to 30 μm in the scanning direction and a width ranging fromapproximately 1 to 5 μm in the direction perpendicular to the scanningdirection, which is the crystal grain as large as that formed by the CWlaser. It is also possible to form a semiconductor film having fewcrystal grain boundaries at least in the moving direction of TFTcarriers by forming a crystal grain of a single crystal extending longalong the scanning direction.

When the oscillation at frequency described above is possible, a beamemitted from a laser selected from the group consisting of an Ar laser,a Kr laser, an excimer laser, a CO₂ laser, a YAG laser, a Y₂O₃ laser, aYVO₄ laser, a YLF laser, a YalO₃ laser, a glass laser, a ruby laser, analexandrite laser, a Ti: Sapphire laser, a copper vapor laser, and agold vapor laser can be used as the pulsed beam.

For example, it is possible to use a YVO₄ laser having a energy of 2 W,a oscillation mode of TEM(00), a second harmonic (532 nm), anoscillation frequency of 80 MHz, and a pulse width of 12 ps. Moreover, apulsed laser irradiation apparatus oscillating this laser can be used.In addition, the beam spot can be shaped into a rectangular spot havinga size of 10 μm in its minor axis and 100 μm in its major axis on thesurface of the semiconductor film by shaping the laser light through theoptical system. When oscillation frequency is set to 80 MHz, theinterface between the solid phase and the liquid phase can be movedcontinuously, thereby forming the crystal grain grown continuouslytoward the scanning direction. It is thus possible to form asemiconductor film having few crystal grain boundaries at least in thechannel direction of TFT by forming a crystal grain of a single crystalextending long along the scanning direction.

In other words, in the case of using either continuous or the pulsedlaser beam, uniform laser irradiation can be performed by thegalvanometer mirror or the polygon mirror of the present invention.

1-9. (canceled)
 10. A method for manufacturing a semiconductor devicecomprising the steps of: emitting a laser beam by an oscillator;reflecting the laser beam by a mirror; and crystallizing a semiconductorfilm by irradiating with the reflected laser beam; wherein the mirrorhas a specular body, the specular body being fixed to a shaft so as tobe set on an optical axis of the beam.
 11. The method for manufacturinga semiconductor device according to claim 10 further comprising: forminga gate electrode over the crystalline semiconductor film, and forming animpurity region in the semiconductor film using the gate electrode as amask.
 12. The method for manufacturing a semiconductor device accordingto claim 10, wherein the laser beam is a beam emitted from any one of aYVO₄ laser, a YAG laser, a YLF laser, a YAlO₃ laser, and an Ar laser.13. A method for manufacturing a semiconductor device comprising thesteps of: emitting a laser beam by an oscillator; reflecting the laserbeam by a mirror; and crystallizing a semiconductor film by irradiatingwith the reflected laser beam; wherein the mirror has a specular body,the specular body being fixed to a shaft so as to be set on an opticalaxis of the beam and rotating on the shaft as its center.
 14. The methodfor manufacturing a semiconductor device according to claim 13 furthercomprising: forming a gate electrode over the crystalline semiconductorfilm, and forming an impurity region in the semiconductor film using thegate electrode as a mask.
 15. The method for manufacturing asemiconductor device according to claim 13, wherein the laser beam is abeam emitted from any one of a YVO₄ laser, a YAG laser, a YLF laser, aYAlO₃ laser, and an Ar laser.
 16. A method for manufacturing asemiconductor device comprising the steps of: emitting a laser beam byan oscillator; reflecting the laser beam by a mirror; and crystallizinga semiconductor film by irradiating with the reflected laser beam;wherein the mirror has a specular body, the specular body being fixed toa shaft so as to be set on an optical axis of the beam and fullyrotating on the shaft as its center.
 17. The method for manufacturing asemiconductor device according to claim 16 further comprising: forming agate electrode over the crystalline semiconductor film, and forming animpurity region in the semiconductor film using the gate electrode as amask.
 18. The method for manufacturing a semiconductor device accordingto claim 16, wherein the laser beam is a beam emitted from any one of aYVO₄ laser, a YAG laser, a YLF laser, a YAlO₃ laser, and an Ar laser.